Generally, semiconductor chip packages are manufactured by attaching semiconductor chips on a lead frame of copper and then electrically connecting the semiconductor chips with wire. The semiconductor chip packages may be divided into the quad flat package (QFP), the pin grid array (PGA) and the ball grid array (BGA) according to manufacturing methods and characteristics of semiconductor chip packages. Particularly, the BGA packages which are direct mounting type packages without a lead frame so as to allows high integration, will be under growing demand in consideration of the technical characteristic of the semiconductor industry which is in a trend of getting preciser.
The BGA packages use a substrate which is formed by laminating a multitude of thin resin sheets to a predetermined thickness through adhesive and cutting the resultant lamination to have a proper width by using an end mill. However, as the substrate mentioned above was formed of multi-layered resin sheets, it was difficult to obtain a uniform thickness. Besides, there was a disadvantage that the cutting face was not accurately straight.
The nonuniform thickness of a substrate and the poor straightness of a cutting face as mentioned above cause a flash due to the molding resin which leaked out through uneven crevices between an upper and lower form-imparting molds and a substrate at the time of molding semiconductor chip packages. FIGS. 1 and 2 show a flash 103 due to a thickness error 105 of a substrate 100 at the time of molding semiconductor chip packages and a flash 102 due to a straightness error 104 resulted from the cutting of a substrate 100.
The flashes in the molding process of semiconductor chips as explained above constitutes a serious cause for production of defective products in the later cutting and packing stages in the course of producing semiconductor chip packages. Therefore, in an effort to reduce those thickness errors in substrate plates, there were employed, for example, such methods in which the corresponding parts of molds were replaced every time of molding or respective substrates were classified based on the thickness groups in order to compensate for the thickness difference among molds. However, these methods still resulted in thickness difference of 1-3 mils for each unit package, even when compensation was made by a cavity bar for each unit substrate, whereby the generation of flashes on individual semiconductor chips could not be avoided and delay in replacement entailed a big loss in productivity.